Wastewater treatment systems typically incorporate a clarifier. For example, the clarifier may be a settling tank, wherein suspended solids in the influent stream are allowed to settle and are continuously removed from the bottom of the tank in the form of a sludge. The sludge contains bacteria and other microorganisms capable of digesting the organic matter found in sewage. A portion of the sludge can be introduced upstream in the wastewater treatment system and is referred to as “return activated sludge” or RAS.
Various devices have been developed to remove the sludge from the bottom of the clarifier where it has settled. For example, the sludge may be removed by suction generated by a head differential, siphon, pump or combinations thereof.
Zhou—U.S. Pat. No. 6,371,308 B1, discloses a system of stationary collection tubes arranged at the bottom of the clarifier. A rake sweeps the bottom of the clarifier to move the sludge to orifices distributed along the collection tubes.
Pentz et al.—U.S. Pat. No. 3,797,664 and Fruchtbaum et al.—U.S. Pat. No. 5,490,920 disclose one or two vertical suction pipes that are supported on a trolley above the surface of the liquid in the clarifier. The trolley traverses from the center of the clarifier to the perimeter of the clarifier, to vacuum sludge off of the bottom.
Bradley et al.—U.S. Pat. No. 5,219,470 disclose a “collection box” mounted on the central column of the clarifier. A suction pipe extends from the bottom of the clarifier to the collection box. The collection box and the suction pipe revolve together around the central column, to sweep the bottom of the clarifier. The collection box is submerged in the liquid within the clarifier and sealed, to create suction. A valve controls the flow of sludge to the collection box. The valve handle (37) is accessible from the bridge or walkway above the clarifier.
Rather than the suctions pipes feeding directly into a central collection box, the suction pipes may be connected to and feed into a trough, for example, through openings in the bottom of the trough, and the trough feeds into a central receptacle. The trough may revolve around a central pier, allowing the suction pipes to sweep along the bottom of the tank. The flow rate of sludge into the trough may be adjusted by partially covering the openings in the trough with a plate. In operation, adjusting the flow rate of sludge into the trough typically involves lowering the liquid level in the clarifier to expose the bolts securing the plates, loosening the bolts, repositioning the plates and re-tightening the bolts.
The pipes or other conduits employed to draw the sludge from the bottom of the clarifier are susceptible to clogging. Booty U.S. Pat. No. 4,094,785 discloses a suction clarifier employing a siphon-type method. During operation, if the suction pipe becomes clogged, differential pressure builds, causing increased suction, which is usually strong enough to clear the clog. Nevertheless, in extreme cases, the clog must be attended to by an operator.
Despite the proliferation of sludge removal devices and methods, a need exists for a system that can readily control and adjust the rate of removal of sludge from the clarifier and can be conveniently serviced, for example, to unclog the suction pipes.